For more than a century, scientists have been fascinated by the possibility that hidden, minuscule spatial dimensions could be influencing the physics of our familiar three-dimensional world. Despite decades of experimental searches, however, there has yet to be concrete evidence of these extra dimensions. Now, a recent study proposes a way to advance this search: using the upcoming Deep Underground Neutrino Experiment (DUNE) to probe these hidden dimensions through neutrino behavior.
Neutrinos are among the universe’s most elusive particles, earning them the nickname “ghost particles.” There are three known types — or “flavors” — of neutrinos, each with a mass billions of times smaller than an electron’s. These particles are remarkable in their ability to transform — or oscillate — into different flavors as they travel through space, even without interacting with other particles.
Studying neutrinos with DUNE
DUNE is a forthcoming neutrino oscillation experiment based in Illinois and South Dakota. “In this experiment, neutrinos are generated by a particle accelerator at Fermilab [in Illinois], travel a distance of 1,300 kilometers [800 miles], and are observed using a massive underground detector in South Dakota,” Mehedi Masud, a professor at Chung-Ang University in South Korea and co-author of the study, told Live Science via email.
The experimental setup is ideal for studying neutrino oscillations. Neutrinos created in Fermilab’s collisions — primarily muon neutrinos (one of the three flavors) — will traverse Earth to reach the South Dakota detector. Along the way, some of these particles are expected to transform into the other two flavors: electron neutrinos and tau neutrinos.
By observing how the different flavors evolve during their journey, DUNE scientists hope to unravel several fundamental questions in neutrino physics, such as the hierarchy of neutrino masses, the precise parameters governing oscillation, and the role neutrinos may have played in creating the matter-antimatter imbalance in the universe.
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The study, published in the Journal of High Energy Physics in November, proposes that the enigmatic behavior of neutrinos could be explained if, in addition to the familiar three dimensions of space, there exist extra spatial dimensions on the scale of micrometers (millionths of a meter). While tiny by everyday standards, such dimensions are remarkably large compared with the femtometer (one-quadrillionth of a meter) scales typical of subatomic particles.
“The theory of large extra dimensions, first proposed by Arkani-Hamed, Dimopoulos, and Dvali in 1998, suggests that our familiar three-dimensional space is embedded within a higher-dimensional framework” of four or more dimensions, Masud explained. “The primary motivation for this theory is to address why gravity is vastly weaker than the other fundamental forces in nature. Furthermore, the theory of large extra dimensions offers a potential explanation for the origin of the tiny neutrino masses, a phenomenon that remains unexplained within the Standard Model of particle physics.”
If extra dimensions exist, they could subtly alter neutrino oscillation probabilities in ways detectable by DUNE, according to the study authors. These distortions could appear as a slight suppression of expected oscillation probabilities and as small oscillatory “wiggles” at higher neutrino energies.
In this study, the authors considered the case of a single additional dimension. The effects of an extra dimension are determined primarily by its size. This dependence creates an opportunity for researchers to investigate the presence of such dimensions by analyzing how neutrinos interact with matter within the detector. The extra dimension influences the oscillation probabilities of neutrinos, which, in turn, can reveal valuable clues about its potential existence and properties.
“We simulated several years of neutrino data from the DUNE experiment using computational models,” Masud said. “By analyzing both the low-energy and high-energy effects of large extra dimensions on neutrino oscillation probabilities, we statistically assessed DUNE’s ability to constrain the potential size of these extra dimensions, assuming they exist in nature.”
The team’s analysis suggests that the DUNE experiment will be capable of detecting an extra dimension if its size is around half a micron (one-millionth of a meter). DUNE is currently under construction and is expected to begin data collection around 2030. After several years of operation, the accumulated data will likely be sufficient for a comprehensive analysis of the theory of large extra dimensions. The team expects the results of this analysis to be available roughly a decade from now.
Additionally, they think that, in the future, combining data from DUNE with other experimental methods — such as collider experiments or astrophysical and cosmological observations — will enhance the ability to investigate the properties of extra dimensions with greater precision and accuracy.
“In the future, incorporating inputs from other types of data could further tighten these upper bounds, making the discovery of large extra dimensions more plausible, should they exist in nature,” Masud said. “Beyond being an exciting avenue for new physics, the potential presence of large extra dimensions could also help DUNE measure standard unknowns in neutrino physics more precisely, free from the influence of unaccounted-for effects.”
